CODEWITHSUNDEEP
nlog
Bagzli
Bagzli

Reputation: 6579

NLog logs Error twice in same file

I am trying to figure out why NLog logs my error twice.

here is my config file:

<nlog xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <targets>
    <target name="debug" xsi:type="File" FileName="DebugTestFile.log" layout="${message} ${exception:format=tostring}" />
  </targets>
  <rules>
    <logger name="*" level="Debug" writeTo="debug" />
  </rules>
</nlog>

Now when I call NLog.Debug(myException); the output is my exception gets printed twice.

If I call NLog.Debug(myException, "My Test Message String"); then the error gets printed out once along with my test message.

What exactly am I doing wrong? According to https://github.com/NLog/NLog/wiki/How-to-Log-Exceptions my configuration is correct.

I tried changing my layout to the following: layout="${message} and when I ran NLog.Debug(myException); it only printed the error once.

However now when I ran NLog.Debug(myException, "My Test Message String"); it only printed my message without the error that comes from exception.

Could this be a bug with NLog?

Upvotes: 5

Views: 5232

Answers (3)

Rolf Kristensen
Rolf Kristensen

Reputation: 19867

NLog Logger-method Error<T>(T value) is shorthand for Error("{0}", value).

This means the ${message} output becomes string.Format("{0}", value) or value.ToString(), which is the original behavior.

NLog have over time tried to improve the handling of Exception-object as value:

But yes a workaround is calling Logger.Error(ex, ""), then ${message} will output empty-string "".

Alternative with NLog v4.6 (and newer) then one can use ${message:withException=true} instead of ${message} ${exception:format=tostring}

Upvotes: 0

Rolf Kristensen
Rolf Kristensen

Reputation: 19867

Updated Answer

NLog.Web.AspNetCore v4.8.6 changes registration of NLog Logging Provider, so one is now allowed to call both AddNLog and UseNLog without experiencing double logging.

NLog 5.0 implements validation of incorrect duplicate target configuration, so one will not experience double logging when using incorrect NLog configuration.

Original Answer

If you are using NLog in AspNetCore, then the problem can be caused by calling UseNLog together with AddNLog or ConfigureNLog.

You should only use UseNLog together with NLog.Web.LogBuilder.ConfigureNLog (Stop using AddNLog):

https://github.com/NLog/NLog/wiki/Getting-started-with-ASP.NET-Core-2#4-update-programcs

Upvotes: 17

Abhinav Saxena
Abhinav Saxena

Reputation: 3914

This is seems to be because of rule in config file, just change writeTo for each logger, in my case I was able to reolve this issue by following same steps:

Example:

Earlier config file which was having issue:

<rules>
  <logger name="*" minlevel="Info" writeTo="console" />
  <logger name="*" minlevel="Error" writeTo="console" />
</rules>

Corrected config file:

<rules>
  <logger name="*" minlevel="Info" writeTo="console" />
  <logger name="*" minlevel="Error" writeTo="console1" />
</rules>

Upvotes: 1

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